First, the placement height of the placement machine The effect of patch height on smt placement is mainly due to the too high or too low placement position will affect the patch pressure, thus affecting the smt placement quality, please refer to the following for the patch pressure. 1. The thickness of the component exceeds the range of the placement machine; 2. The mounting shaft is loose; 3. The use of special-shaped components or shaped nozzles.
Second, the placement pressure of the placement machine Patch pressure is another key factor that needs to be controlled. For chip components and leaded ICs, improper patch pressure control can result in component damage, solder paste collapse, solder beads under the component, and potential component offsets, for example, mounting 0201 and The 01005 component has a suitable pressure range of 150 to 300 g. For the special-shaped plug-in components (multi-function machine), if the pressure is too small, the components will not be able to be embedded in the positioning holes, such as the mounting of the mobile phone shielding cover and the computer motherboard connector. In special cases, the maximum pressure required may reach 2.5 to 5.0. Kg. In addition, for the case of PCB deformation, the patch axis must be able to sense changes in pressure corresponding to deformations as small as 25.4 μm to compensate for PCB deformation. Excessive pressure can cause a horizontal force on the component during the depression (due to bending of the PCB deformation), causing the component to slide laterally. In addition, excessive pressure will squeeze the solder paste at the bottom of the component to form solder balls or cause adjacent components to be short-circuited. Third, the vacuum suction of the placement machine Most of the placement machines use a vacuum generator to generate a negative pressure in the suction of the chip components and the IC. For the placement system, the vacuum suction is not only greater than the gravity of the component, but also meets the motion (acceleration) requirements of the placement head. If the vacuum suction is small, after the component is recognized by the camera, the placement head moves to In the process of placing the dots, it is very likely that the components will be offset, which will directly lead to the placement bias. After the smt patch proofing or processing and soldering, it is easy to produce defects such as the monument. The following formula is the vacuum suction formula F = PS (5-1), where P is the negative pressure generated by the vacuum valve, and S is the effective contact area of the nozzle. The normal working pressure of the vacuum valve depends on the air pressure of the system air source and the atmospheric pressure (related to the altitude). At present, most of the placement machines have a gas source pressure requirement of 60 to 90 PSI, which is related to the characteristics of the equipment. In addition, the effective contact area of the nozzle is determined by the type of the nozzle and is also directly related to the degree of wear of the suction surface. If the effective contact area is too small due to the wrong type of the nozzle, this will directly reduce the vacuum suction. In addition, if the wear of the suction surface is too large, the gas leakage will cause a serious decrease in the P value, which also affects the vacuum suction. Therefore, when the user suspects that the suction or the component has slippage on the placement head, the degree of vacuum and the factors related to the degree of vacuum should be preferentially checked, or these items should be regularly inspected during the production process to control the placement quality. Fourth, blowing At the final stage of the process of placing the head-mounted components, when the placement head places the component at a given height, the vacuum is turned off and then there is a brief blowing action. The purpose of the process is to completely eliminate the nozzle pipe. The negative pressure in the middle ensures that the component does not stick to the nozzle at the moment the nozzle is raised, so that the component is not carried away or displaced on the solder paste. If the action process fails to occur in time, the impact is conceivable. In addition, the blowing time should not be too long, otherwise it may affect (blow) adjacent components or blow away the solder paste.
